Learn about Senior Chemistry: Equilibrium 1 Video

Rob Lederer: As you learn more and more chemistry, you find out that things that we teach you in the past, kind of get changed around to become either better explained or we clear up some of the lies that we've taught you. for instance, all the reactions that we write all the time have this arrow pointing from reactions to products that says, look these things make this and for all we know, this was a 100% reaction all the time. But, you know what? We've also talked about how reactions can be reversed and if that's true, maybe reactions can actually be reversed at any given time in an enclosed container. They can and that causes all kinds of interesting chemistry. Take for instance, if you have a bag full of H2 molecules, and then a bag full of I2 molecules then you are all balancing around in here. Collision theory is going to tell us that as molecules collide with sufficient force, we can reach a certain activation energy and get them to maybe even separate the Hs from each other and the Is from each other. Now that might recombine and form H2s and I2s again, but they could actually mix together and form HIs in that container. Now, here is the thing. So, that makes perfectly good sense. But, interestingly at any given temperature, what will eventually happen in these enclosed containers is that we will get virtually a consistent amount of HI after a certain period of time in here, in comparison to how much I2 and H2 is left, and that's where we've reached something called equilibrium. The definition of equilibrium, chemical equilibrium is that, the concentration of reactants like H2 and I2 here remain constant over time. And so will be the products, the HI amount remains constant over time, when reactants and product concentrations remain consistent over time. Now, we are talking about rate, in terms of, if we add a little bit of heat, maybe the rate of reaction will go up. But, the point is about equilibrium is that, at any given temperature, the rate of forward reaction equals the rate of reverse reaction. When you've got that happening, then you have to have the consistent amounts of products and reactions over time and that again is equilibrium. We have talked about that as being in a closed container. Equilibrium must be in a closed system. You cannot have matter entering and leaving and call that equilibrium because, it just won't be. But, if in a closed system, you have a rate of forward reaction equaling each other. Now that is consistent and equilibrium. So, it has to be in a closed container or closed environment. You cannot have matter passing in and out. Energy can, so it's not a completely isolated system, but it is closed. So, those are the definitions for equilibrium. Aside from the fact that once we've achieved equilibrium, the particles are just sitting still because, you still have to have a rate of forward and reverse reaction. So, equilibrium is a dynamic process, not static. We can actually put an equilibrium system into the water and well, we start off by putting some salt into water and stirring it around. Now, here is what you know and is probably from your junior chemistry course. That is stirred out around and eventually, when all of the solute dissolves into the solvent to make the solution, that you can have here an unsaturated condition, if you can still dissolve more crystals into the solution. Then that is unsaturated, but it's not equilibrium. What we have to is we have to dump a lot in, and then eventually even though we are really stirring vigorously, no more solute dissolves into the solvent to make a solution; that's when we have actually an equilibrium situation. Now, again at the bigger level, big view macroscopic. I don't know what's happening, not pretty much. But at the microscopic level, there are crystals that are remaining on the bottom that are actually dissolving in at the same time that dissolved solute is reentering into the solid phase. And so, what we have there is the rate

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